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Submitted to: National Sedimentaton Laboratory (NSL)- 50 Years of Soil & Water Research in a Changing Agricultural Environment
Publication Type: Proceedings Publication Acceptance Date: 7/31/2008 Publication Date: 9/26/2008 Citation: Langendoen, E.J. 2008. Assessing the impact of riparian processes on streambank erosion. National Sedimentaton Laboratory (NSL)- 50 Years of Soil & Water Research in a Changing Agricultural Environment. pp. 814-830.. Interpretive Summary: Pollutants such as nutrients (nitrogen and phosphorus) and soil, washed off agricultural fields or eroded from stream channels, may diminish the water quality of streams and rivers. The stream and the area between stream and agricultural field, the riparian zone, play an important role in the management of pollutants. The vegetation in the riparian zone is also known to reduce erosion from the streambank due to bank material strengthening by plant roots and the removal of groundwater. The U. S. Department of Agriculture-Agricultural Research Service has been developing the computer models REMM and CONCEPTS to study the effects of riparian forests or buffers and in-stream conservation measures on water quality. These models have been integrated to provide a comprehensive tool that can be used to assess the effects of riparian buffers on the physical and biological integrity of a stream. Initial application of the model to a severely eroded stream in North-Central Mississippi showed that it can satisfactorily simulate the processes that control streambank erosion. However, some discrepancies were observed in the simulated lateral movement of groundwater. Various groundwater models of different complexity were tested to determine how accurately they could simulate the lateral movement of water in streambanks constructed in a laboratory. Results show that models that can accurately simulate the movement of groundwater in the saturated area of a streambank performed well. Work is ongoing to include these models in the REMM model to produce an improved tool that can be used by state and federal agencies to assess vegetative, riparian conservation measures. Technical Abstract: Soil water dynamics within a streambank and riparian vegetation greatly affect streambank erosion. The integrated computer models CONCEPTS and REMM, which were developed to simulate stream channel morphology and riparian ecosystem function, were previously used to study the effectiveness of woody and herbaceous riparian buffers in controlling streambank stability of streams in Mississippi. Model results showed that pore-water pressures are accurately predicted in the upper part of the streambank, away from the groundwater table. Results further depended on imposed soil permeability, which is greatly affected by the development of macropores and cracks in the dry summer and fall period. To improve the capabilities of the above-mentioned integrated model, subsurface flow formulations that can be used to evaluate the effects of pore-water pressures on streambank stability at different temporal scales are presented and tested. To resolve the movement of wetting and drying fronts and their impact on bank stability temporally (i.e., time scales ranging from minutes to hours), a model based on the Richards equations describing unsaturated flow is needed. However, if streambank stability assessment uses time intervals of one day or larger, over which the pore-water pressure distribution may have reached a quasi-equilibrium state, the use of simpler models, such as those based on the Boussinesq equation, can accurately predict subsurface flow and pore-water pressure. |
